Polycyclic Aromatic Hydrocarbons (PAHs) are a class of persistent organic pollutants characterized by two or more fused aromatic rings. They originate primarily from incomplete combustion of organic matter (e.g., fossil fuels, biomass, waste) and pyrogenic sources (e.g., industrial processes, vehicle emissions), as well as petrogenic sources like crude oil spills and natural seeps (The most important source of aromatic hydrocarbons is gaseous waste from oil fields) [1]. Due to their hydrophobic nature and low solubility, PAHs readily adsorb to suspended particles and accumulate in aquatic sediments, acting as long-term reservoirs of contamination [2]. This persistence poses significant ecological and human health risks, as many PAHs are carcinogenic, mutagenic, and toxic to aquatic organisms [3].

The Tigris River, a vital freshwater resource in Iraq, sustains agriculture, industry, and domestic needs along its course. At Amara City in southern Iraq, the river is exposed to multiple anthropogenic pressures. Rapid urbanization, industrial discharges, untreated municipal sewage, agricultural runoff, vehicular emissions, and historical conflict-related pollution contribute) damage caused by historical political, military, or social conflicts in the region, which have indirect but severe environmental consequences. These conflicts often lead to poor infrastructure maintenance, particularly drainage systems, resulting in inadequate wastewater management and increased pollutant discharge into water bodies(. Human activities, such as unauthorized dumping, intensified agriculture, and industrial neglect during and after conflicts, exacerbate the pollution load. The cumulative effect is significant environmental degradation affecting water and sediment quality to the degradation of water and sediment quality [4]. Additionally, reduced river flow due to upstream damming exacerbates pollutant accumulation in sediments. These factors create a critical need to assess sediment contamination, as sediments reflect historical and ongoing pollution and can release toxins back into the water column under changing conditions [5].

Monitoring PAHs in the sediments of the Tigris River at Amara City is essential for several reasons: (1) identifying contamination hotspots and sources; (2) evaluating ecological risks to benthic organisms; (3) informing public health strategies for communities relying on the river; and (4) guiding remediation efforts. Despite its importance, comprehensive data on PAH levels in this specific reach of the Tigris remains limited. This study therefore aims to quantify the concentration, composition, and spatial distribution of PAHs in sediment samples collected from the Tigris River at Amara City, southern Iraq. Consequently, this finding will contribute to a baseline understanding of contamination, support ecological risk assessments, and aid in developing targeted management strategies for this crucial ecosystem.

Study Area and Sampling Stations

Five stations were selected along the Tigris River at Amara City, Maysan Province (Fig 1, Table 1). Samples were collected systematically to represent riverine conditions affected by urban and industrial inputs.

Analytical Methods

Sedimentsamples were dried in an oven at 50 °C, grinded finely in an electrical mortar and sieved through a 63 µm mesh sieve, stored in glasses containers until analysis. 50 grams of sieved sediment were placed in cellulose thimble and extracted by using Soxhlet intermittent extraction according to the method of Goutx and Saliot, 1980 and Saleh et al., 2021 [6][7] by adding a mixture of solvents (120 ml) methanol: benzene (1:1 v/v) for 48 hrs. at temperature doesn’t exceed 40ᵒC. The combined extracts were saponification for 2 hrs. by adding (15ml) 4M MeOH (KOH) at the same temperature and cooled to room temperature. The un saponification matter was extracted with (50 ml) n-hexan using separator funnel. a 20 cm glass column packed with glass wool, 8 g silica gel (100-200 mesh), 4 g aluminum oxide (Al₂O₃, 100-200 mesh), and 4 g anhydrous sodium sulfate (Na₂SO₄) at the top. The Aromatic component was eluted by using benzene.

GC-MS examination of PAH compounds was performed using an Agilent 7890B gas chromatograph interfaced with an Agilent 5977A mass spectrometer. The temperature schedule of the GC oven was: starting temperature of 40°C, ramped at a rate of 10°C/min to a final temperature of 310°C. The injector temperature was set to 260°C by employing split mode (ratio 75:1). The flow control was set to constant flow with the pressure of 7.0699 psi, total flow of 79 mL/min, column flow of 1 mL/min, and purge flow of 3 mL/min.

Mass spectrometer conditions: ion source temperature 250°C, quadrupole temperature 150°C, interface temperature 280°C. Solvent cut time was constant at 4.00 minutes, with start time 4.00 minutes and end time 35.00-40.00 minutes. Individual PAH compounds were identified by comparison of retention times and mass spectra with authentic standards and the NIST mass spectral library. Quantification was done by external standard calibration using PAH standards.

Different PAH profiles at specific Amara stations are mainly due to local pollution sources, differences in human activities along the river, episodic contaminant inputs, and varying sediment characteristics. While the overarching PAH composition is similar (dominated by HMW compounds, reflecting comparable sources), there are notable differences in the abundance of specific PAHs between stations—most strikingly for Dibenzo[a,h]anthracene at station 5 and slight increases in Benzo[k]fluoranthene and Chrysene downstream. These differences may result from varying local sources, land use, or point-source discharges affecting specific sites. The distribution of PAH concentrations among the five stations in Amara City reveals a trend of moderate increase from the uppermost station (Station 1) to a maximum at Station 5, These findings reflect local influences and suggest both urban runoff and industrial discharges are key contributors to sediment contamination in this region.

Recommendations

Enhance continuous PAH monitoring in Tigris sediments. Enforce stricter industrial waste management and emission controls. Promote public awareness regarding risks linked to PAH contamination. Develop ecological risk assessment protocols specific to southern Iraq’s riverine system.and also

Establish a national pollution database.,

·Track the main sources of pollutants

· Assess toxin accumulation in fish

· Activate and tighten environmental laws

· Develop emergency plans for spills

· Enhance regional cooperation with basin countries

· Utilize water treatment technologies

· Support local research

· Raise awareness among farmers

· Plant trees along riverbanks